Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 082025
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
325 PM EST Thu Dec 8 2016

.DISCUSSION...

Snow squall activity around this afternoon will be
diminishing/decreasing in coverage as sharp shear axis/trough swings
south through the Central Great Lakes this evening, allowing for
wind shift to the northwest and general subsidence and a drying out
process (some breaks in cloud cover). However, there looks to be a
good chance for a dominate/narrow Lake Superior-Lake Michigan band
to set up overnight into Friday, as average 925-850 mb temps looks
to be lowering to favorable -10 to -12 C range. 12z Regional GEM
most aggressive with the band Impacting Tri-Cities into Flint
Vicinity, while the HRRR is farther west. 12z nam appears to be the
farthest east, with northern Thumb region being impacted on Friday.
Inversion heights look to be at or above 7 kft, which favors the
case for band(s) reaching southeast Michigan. Narrow nature of the
band and uncertainty with movement makes for difficult call on
amounts, but potential for localized amounts greater than 1 inch is
there as we get into the tail of the upper level pv lifting
northeast, providing some support during Friday, with near saturated
and cold 700 mb temps of -20 to -23 C. Backing flow in the afternoon
will also likely bring some snow shower activity back into the I-94
corridor as well.

Upper level northwest confluent flow Friday Night/Saturday, but
westerly flow and 850 mb temps still hovering in the negative mid
teens will continue to support flurries or light snow showers.

Warm advection/Fgen Saturday Night will bring increasing chance of
light snow by Sunday Morning. Favorable thermal profiles and 850 mb
specific humidity approaching 2 G/KG suggest a few inches possible.

A brief lull from snow will be possible throughout the late morning
to early afternoon hours. Any periods or little to no snow will be
short-lived as low pressure centered over northern Texas/Oklahoma
early Sunday will begin to push northeast into the Ohio Valley into
early Monday. The chance for snow will once again increase
throughout the late afternoon to early evening hours on Sunday, with
the chance for snow continuing into Monday morning. While we are
starting to narrow down on timing of the system as models converge,
uncertainty still exists regarding placement of the low. The GFS and
ECMWF models have flip-flopped over the past 24 hours, with the GFS
model bringing the low more north, clipping SE MI Monday morning and
afternoon. This allows SE winds to pool in warmer air into the
region, allowing 850 mb temperatures to straddle the 0 degree
isotherm during the morning, which has the potential to influence
precipitation type.  Both the ECMWF and GEM models keep the low just
south, tracking across Ohio throughout Monday morning, keeping
conditions much cooler and allowing precipitation to remain as snow.
We will likely be a day off before issuing snowfall estimates for
Monday`s snow, as models continue to converge, however, it`s safe to
assume accumulation totals will impact travel Sunday through Monday.
Snow from this system will taper off late Monday, however, a shift
in winds from northeast to east will bring additional chances for
lake effect snow throughout the early part of the week. The second
main story for the extended will be the advent of polar air, which
looks to take daytime high from the lower 30s to upper 20s during
the early part of the week, to the upper 20s to lower teens by mid-
week.

&&

.MARINE...

Existing near gale conditions across the southern Lake Huron waters
will gradually ease early tonight as the become more northwesterly
with a frontal passage.  This will maintain small craft advisory
conditions for all near shore waters into tonight.  This will shift
to northwesterly will introduce a greater potential for snow squall
development tonight into Friday.   Building high pressure south of
the Great Lakes will then allow moderate winds to take hold for the
end of the week before the arrival of the next low Sunday into
Monday.

&&

.PREV DISCUSSION...
Issued at 116 PM EST Thu Dec 8 2016

AVIATION...

Existing environment to sustain favorable conditions for lake effect
snow shower development and downstream penetration through the
evening hours. Bursts of heavier activity will continue to result in
intermittent reduction of visibility into IFR.  Westerly winds
remain gusty through this time, contributing to these visibility
restrictions within any snow showers.  Mixed signal on prospects to
maintain a greater coverage of snow showers tonight, as the flow
becomes more northwesterly with the passage of a frontal boundary.
Given this, will let near term trends dictate the need for a more
defined mention beyond 03z tonight.

FOR DTW...Terminal will remain susceptible to brief bursts of
heavier snow showers through the early evening period.  While these
bursts will remain transient, this could result in rapid/brief
disruptions to visibility below 1 mile and a dusting of
accumulation as the burst occurs.

//DTW Threshold Probabilities...

* High for ceiling 5000 ft or less through tonight.

* High for snow as precipitation type.

* Low for visibility dropping to 1/4 mile or less in snow showers
  through this evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 10 PM EST this evening FOR LHZ422.

     Small Craft Advisory until 10 AM EST Friday FOR LHZ441>443.

     Small Craft Advisory until 6 AM EST Friday FOR LHZ421.

Lake St Clair...Small Craft Advisory until 10 PM EST this evening FOR LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EST this evening FOR LEZ444.

&&

$$

DISCUSSION...SF/AM
MARINE.......MR
AVIATION.....MR


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